Niyato. In my four years doctoral program, when I came across big difficulties in the research, Prof. Dusit Niyato always taught me to analyze these difficulties from a different perspective. When I felt frustrated and lost my confidence, he gave me a lot of inspiration. Besides, he sets me a good example on how to be a qualified researcher. He taught me the method of searching useful information among huge data, the experience of mastering mathematical tools, and the good habit of managing time more efficiently. Moreover, he pointed out on the novel research direction which leads me to my research road and gave me a lot of enlightenment on specific details in my research works. Secondly, I would like to express my deep gratitude to my co-supervisor, Prof. Ping Wang for her invaluable guidance and suggestions on my research project as well as on my attitude about communicating with people and facing difficulties in the life. She and her family also treated me and my group members dinners when we were homesick on Chinese traditional festivals. Thirdly, I express my sincere thanks to Prof. Zhu Han. He shared a lot of interesting ideas with me and also gave me invaluable instructions on my research. Besides, I would like to thank our research group members and lab colleagues. We spent happy four years together. The technicians in my lab are all very friendly too. Special thanks for their self-giving help and warmhearted assistance on research facilities. As a Ph.D. student, I am also very grateful to my university and school for the opportunity they gave to me so that I can come to Singapore, open my eyes to the wonderful research field, and have the chance to be connected with the world. Finally, I wish to express my deepest gratitude to my parents for their everlasting love, encouragement and support in my life.